The invention relates to a key input control apparatus used for a small sized electronic calculator.
Some electronic calculators such as desk-top type electronic calculators are provided with an extra key, for example a .pi. key. When the .pi. key is depressed, the numeral "3.1415 . . . " is keyed in by a single keying operation in place of a plurality of keying operations of the ten keys representing the respective numerals `3`, `1`, `4`, `1`, `5`, . . . of "3.1415 . . . ". When the .pi. key is operated, a calculation as in the case of the ten key operation must be performed. In the calculation of "sin 3/4.pi.", for example, keys are operated in the order of ##EQU1## The key ##EQU2## is a command key to command the calculation of a fraction. Thus, in the conventional calculator, the extra .pi. key is treated like the ten key and therefore the calculation needs the keying operation of a function key to command the calculation after the .pi. key is operated. Therefore, the keying operation is complicated. This creates a problem, particularly in the calculation of polynomial. In other words, in such a calculation, since the keying operation is complicated, the calculation must be carefully performed to avoid erroneous keying operations which are highly possible to occur.
In a calculation requiring a repeat of keying operations of the key, for example, the calculation of ".pi. sin 3/4.pi.", the keying operation is carried out in the order of keys 3 .times. .pi. .div. 4 = sin .times. .pi. = . That is to say, the key operation is very complicated.
Accordingly, an object of the present invention is to provide a key input control apparatus in which an entry function or a calculation function of a special key is selectively executed in accordance with a key operation performed immediately before the extra key with such functions is operated, thereby simplifying the key operation.